The crew of a sailing dinghy normally have considerable difficulty in reading a tactical compass while sailing. This is because the compass is generally mounted centrally within the dinghy yet the crew are on the side of the dinghy and leaning outwardly, or may be suspended by a trapeze, to balance the dinghy and prevent it from capsizing. Under these circumstances a traditional compass marked with numbers or letters or both is extremely difficult, if not impossible, to read.
The crew of a sailing dinghy often must be preoccupied with positioning themselves so as to keep the dinghy upright so that a centrally mounted compass is simply visibly inaccessible. Even if the compass is mounted on the gunwhales of the dinghy, an outwardly leaning crew may not be able to read the numbers or letters on a compass card. These problems are particularly acute in single handed sailing craft such as Laser class dinghys or sail boards where the single crew has both his hands occupied in controlling the sheets and tiller and is often required to position himself well away from a compass.
Further, certain calculations require to be made during a sailing race, using a traditional compass. For example, determining the favoured end of the starting line, detecting wind shifts and calculating headings to the marks all require that the crew exercise mental arithmetic skills. The physical demands of dinghy sailing are such that it is extremely difficult to exercise the arithmetic skills needed to make these calculations. Again, these problems are particularly acute for single handed sailors in for example Laser class dinghys or sail boards.
Compasses having marked tacking angles on adjustable peripheral bezels have been used, however they still require the user to remember numbers and discern whether the numbers are increasing or decreasing as the compass swings, thus allowing the user to know if he is "lifting" or "knocking" on a particular tack.